In a conventional piano, the external force applied when a keyboard is operated results in the movement of a hammer system causing the hammer to strike the string and generate sound. In consideration of housing conditions or the necessity of practicing finger movement, a soft pedal mechanism or a muffler mechanism has been used to soften or dampen the piano tone.
In the soft pedal mechanism, the hammer rail provided at the back of the hammer system is moved by operating a soft pedal, thereby making the distance between hammer and string at their stationary position shorter than that when normal sound volume is generated. The velocity of the hammer at its striking position is reduced, thereby restricting the volume of sound generated by the string struck by the hammer.
In the muffler mechanism, felt or other cushioning material is interposed between hammer and string. The hammer strikes the strings indirectly via the cushioning material, thereby dampening the sound volume.
In the conventional soft pedal mechanism, the distance between hammer and string is restricted. Thus, the distance to be reduced by moving the hammer rail is also restricted. To effectively dampen the sound volume, however, the distance between hammer and string needs to be largely reduced. If the hammer is too close to the string, the feel of the key upon operating the keyboard is changed, or sound may be accidentally generated by the operation of the soft pedal without operating the keyboard.
In the conventional muffler mechanism, since the hammer strikes the strings indirectly via the cushioning material, the tone quality is softened. Hard tone, which is the normal piano tone, cannot be made. Thus, the characteristic piano tone cannot be made.
Conventionally, by combining an acoustic piano with an electronic sound source, electronic sound as well as the normal piano performance can be achieved. But, string striking sound can be prevented from being generated from the electronic sound source by the hammer shank stop rail preventing the hammer from striking the string. If the keys are operated such that the electronic sound is generated based on depressing or releasing the keys, the hammer shank contacts the cushioning felt provided on the hammer shank stop rail before the hammer strikes the string, thereby stopping the movement of the hammer. Therefore, no string striking sound is produced. By using this mechanism together with headphone, a player can play the piano by operating the keyboard and listen to the electronic sound through the headphone, while string striking sound is not heard outside. The piano may be freely played at night or in an apartment house, housing complex or other densely built-up area requiring sound suppression.
In the aforementioned conventional piano, the portion of cushioning felt provided on the hammer shank stop rail corresponding to the hammer's string striking position becomes deformed with repeated use. This is especially true in the case of an often used key. This deformed portion of the cushioning felt cannot stop the corresponding hammer at the originally specified position. Gradually, the deformed portion is worn down so that the hammer is allowed to strike the strings, thereby producing sound.
To avoid the production of string striking sound, the cushioning felt must be replaced often. The replacement is intricate and costly.